refactor: consolidate SDK Watchable with generic map/eq and rename call to fetch

sdk/base/lib/util/GetServiceManifest.ts

@@ -1,18 +1,47 @@
 import { Effects } from '../Effects'
 import { Manifest, PackageId } from '../osBindings'
+import { deepEqual } from './deepEqual'
 import { Watchable } from './Watchable'
 
-export class GetServiceManifest extends Watchable<Manifest> {
+export class GetServiceManifest<
+  Mapped = Manifest | null,
+> extends Watchable<Manifest | null, Mapped> {
   protected readonly label = 'GetServiceManifest'
 
   constructor(
     effects: Effects,
     readonly opts: { packageId: PackageId },
+    options?: {
+      map?: (value: Manifest | null) => Mapped
+      eq?: (a: Mapped, b: Mapped) => boolean
+    },
   ) {
-    super(effects)
+    super(effects, options)
   }
 
-  protected call(callback?: () => void) {
+  protected fetch(callback?: () => void) {
     return this.effects.getServiceManifest({ ...this.opts, callback })
   }
 }
+
+export function getServiceManifest(
+  effects: Effects,
+  packageId: PackageId,
+): GetServiceManifest<Manifest | null>
+export function getServiceManifest<Mapped>(
+  effects: Effects,
+  packageId: PackageId,
+  map: (manifest: Manifest | null) => Mapped,
+  eq?: (a: Mapped, b: Mapped) => boolean,
+): GetServiceManifest<Mapped>
+export function getServiceManifest<Mapped>(
+  effects: Effects,
+  packageId: PackageId,
+  map?: (manifest: Manifest | null) => Mapped,
+  eq?: (a: Mapped, b: Mapped) => boolean,
+): GetServiceManifest<Mapped> {
+  return new GetServiceManifest<Mapped>(effects, { packageId }, {
+    map: map ?? ((a) => a as Mapped),
+    eq: eq ?? ((a, b) => deepEqual(a, b)),
+  })
+}